DATE：2020-03-02source：ZhouSanZhengYu
N95 mask - powerful 95% filtration efficiency
N95 mask can filter most of haze, dust, pollen, influenza virus, smoke and dust in automobile exhaust, and the filtering efficiency should be at least 95%. N stands for not resistant to oil, i.e. not oil resistant, and 95 stands for the filtration efficiency level of 0.3 micron particles when tested.
N95 mask with breathing valve
Internal structure of N95 mask
cutting off the N95 mask, we can see that its internal structure mainly has three layers, among which the key layer plays a role of barrier is the 290000 / t melt blown cloth in the market.
100 times magnification to see the melting and spraying cloth of mask
We can see that the melt blown cloth is made up of numerous microfibers, which are overlapped into a dense network.
100 times magnification (mask melt blown cloth, Olympus microscope)
Among them, the thickness of each fiber is about 1-5 microns, and the fiber is complex, which can prevent dust, virus and bacterial micro foam from entering, while maintaining the hole through which the breath passes. Therefore, it not only meets the requirements of filtration efficiency, but also meets the requirements of respiratory resistance.
There is no harm without comparison. Take the ordinary non-woven fabric for comparison. Under the microscope, although the fiber looks more uniform and beautiful, the diameter of the fiber is more than 20 microns, and the gap is much larger. In this way, the non-woven fabric effectively blocks viruses, bacteria and small particle dust.
100 times magnification (ordinary non-woven fabric, taken under Olympus microscope)
N95 mask cloth - Electrostatic addition (electret treatment)
The melting and spraying layer of N95 respirator is not dense enough, and static electricity needs to be increased through electret discharge treatment. In a certain range, the larger the applied voltage (electret voltage), the stronger the charge is bound, and the higher the filtering efficiency.
Electret discharge treatment of melt blown cloth
Electret processing - electret Masterbatch
The surface charge of the melt blown cloth will decay with time. When the electret masterbatch is added, the decay time is greatly prolonged. With the proper increase of the electret masterbatch, the charge retention rate is also longer, and the decay rate of different electret masterbatch formulations is different.
Note: from the literature, to explain the problem of charge decay
The electret masterbatch (usually 2-3%) separates the positive and negative charges of PP microfiber and holds them for a longer time.
Polarized fiber
The production enterprises of electret masterbatch are few, most of them are the masterbatch factories supporting melt blown cloth, and the scale is usually small.
Experience has been accumulated in long-term production. A large number of exploratory tests have been carried out on the formula from the selection of auxiliary agent, basic resin, granulation temperature, screw combination, melt finger control, auxiliary content, etc. in combination with the electret treatment, the filtration performance, filtration resistance and other indicators have been optimized. The melt blown cloth has also been placed for half a year, one year, two years or more to test the filtration performance and other indicators.
Through the melt blown cloth factory and the customer channel, the electret masterbatch manufacturers with better feedback in the market are collected for reference only. The specific application is also related to the melt blown equipment, process and formula of the manufacturers.
Table 1 domestic electret masterbatch manufacturers (to be updated)
Note: the information is recommended by aibang polymer and melt blown manufacturer for reference only, without any legal liability
The maintenance of N95 mask -- the natural enemy of static electricity
As time goes on, the binding force of the charge after electret weakens, the charge will swim away and the polarization effect will weaken. With the passage of time, static electricity will gradually disappear, which is why N95 masks have a shelf life. The general shelf life is about five years. N95 mask is most afraid of water, the secret of maintenance is to stay away from water.
During the protection process of N95 mask, particles are adsorbed and static electricity is consumed. Therefore, after a period of time, a large number of particles are adsorbed, and the static electricity is consumed, so there is no additional static electricity to adsorb particles. That's why used N95 masks can't be reused.
